A mobile HDMI source device having a HDMI output connection can be connected to an HDMI sink such as a television, in order to display pictures or video. In such a use case, it would be very useful for the user to be able to take this opportunity to do power charging of the mobile device.
FIG. 1 shows the components of an HDMI version 1.4 system. The different features are discussed in turn:
TMDS Channels
Four TMDS (Transition Minimized Differential Signaling) signals are provided over 4 twisted pair wires, including 3 digital video signals (RGB or YCrCb) and 1 clock signal. The digital audio signals are also multiplexed into the digital video signals.
The Dual-Link HDMI has 3 more twisted pair wires for digital video signals to achieve higher data rate.
The data is transported via one of three modes, called the Video Data Period, the Data Island Period, and the Control Period. During the Video Data Period, the pixels of an active video line are transmitted. During the Data Island period (which occurs during the horizontal and vertical blanking intervals), audio and auxiliary data are transmitted within a series of packets. The Control Period occurs between Video and Data Island periods.
DDC Channel
The DDC (Display Data Channel) data and clock lines carry the two-way communication signals; the HDCP (High-bandwidth Digital Content Protection) signal also floats here.
The DDC channel is based on the I2C bus specification. HDMI specifically requires support for the Enhanced Display Data Channel (E-DDC), which is used by the HDMI source device to read the EDID (Enhanced display identification data) from a memory in the HDMI sink device to learn what audio/video formats it supports. An extended version E-EDID is also used.
CEC Line
The CEC (Consumer Electronics Control) data line distributes remote control signals. The feature is designed to allow the user to command and control multiple CEC-enabled boxes with one remote control, and for individual CEC-enabled devices to command and control each other without user intervention. So called “Capability Discovery and Control” commands (CDC) are sent on the CEC data line/bus.
HPD Line
The HPD (Hot Plug Detection) line allows the source to detect a display plugged in real time. Typically, the HDMI sink connects the HPD line to the 5V power supply received from the source when it is connected, so that its presence can be detected in the source.
The sink asserts a high voltage level on the Hot Plug Detect line as soon as the EDID memory is available to read. This signal indicates to the source that it can use the DDC channel (but not necessarily that the sink is ready to display a picture).
Most of the time, the Hot Plug Detect line is high, because the source needs to read the EDID memory to know the capability of the sink before transmitting any video or audio signal.
Sometimes, a short Low voltage level pulse (at least 100 msec) is asserted on the Hot Plug Detect line. The HDMI sink uses this pulse to indicate when changing input or power status, in order to reset the HDCP engine of the source.
The output impedance of Hot Plug Detect line is 1 kOhm, so the simplest connection between +5V Power line and Hot Plug Detect line is a 1 kOhm resistor (rather than a simple short).
+5 V Power Line
Thus supports remote circuits for communication even when the power is not turned on.
HEAC
The HEAC (HDMI Ethernet and Audio Return Channel) is a high-speed bi-directional channel introduced in HDMI version 1.4, which facilitates 100 Mbps Ethernet capability. The same high-speed channel also includes Audio Return functionality which means that audio can be streamed directly to an A/V receiver over the HDMI cable.
Three pins are assigned to perform this function, independent of the TMDS data and clock channels.
The Utility and HPD conductors form a differential pair which uses the DDC/CEC Ground (the dotted line in FIG. 1) as its shield.
With existing solutions, in order to charge a source device, the user has to plug the power charger on the required connector of the mobile device. For example, a known solution is to connect a USB charger to the USB connector of the device. This means that the user has to connect two cables, which is not very convenient and can even be impossible due to the nearness of connectors on miniaturized mobile devices.
It is therefore an aim of the invention to provide for a more convenient way of charging the mobile device.